[RISCV] Fix build after r315327

Differential Revision: https://reviews.llvm.org/D38779
Patch by Chih-Mao Chen.

llvm-svn: 315455
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp
index 6319db8..2756d65 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp
@@ -11,6 +11,7 @@
 #include "MCTargetDesc/RISCVMCTargetDesc.h"
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCFixup.h"
+#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/Support/ErrorHandling.h"
 
 using namespace llvm;
@@ -61,8 +62,9 @@
   }
 }
 
-MCObjectWriter *llvm::createRISCVELFObjectWriter(raw_pwrite_stream &OS,
-                                                 uint8_t OSABI, bool Is64Bit) {
+std::unique_ptr<MCObjectWriter>
+llvm::createRISCVELFObjectWriter(raw_pwrite_stream &OS, uint8_t OSABI,
+                                 bool Is64Bit) {
   return createELFObjectWriter(
       llvm::make_unique<RISCVELFObjectWriter>(OSABI, Is64Bit), OS,
       /*IsLittleEndian=*/false);